When performing a live migration (kvm) when multi_host is set to True the following does not happen:
1) The networks(bridge and vlan) on the destination node are not setup by nova-network.
*) If this is not configured before the migration the instance will fail to start on the destination node and will rollback to the source node.
2) dnsmasq is not updated on the destination node.
*) dnsmasq hosts file is not updated on the migration destination and it will not reply to DHCP requests from the migrated instance.
*) Additionally, DHCP requests will still be answered by the source migration node until a new instance is created on that compute node. When that happens dnsmasq host files are re-written and dnsmasq is sent SIGHUP and it will no longer respond to DHCP requests from the migrated instance.
If both of the above occur the migrated instance will lose IP access upon the expiration of its lease.
I have included a patch that will fix this in the short-term but a more elegant resolution is required.
Tested and fixed on diablo/stable. This bug is also present in essex.